a) My understanding of the rule of Concord is that the only exception to
the necessary agreement in number between an external subject and its
related finite verb is that a neuter plural subject can take a singular
verb. Correct?

But in Eph.4:31 the main verb 'ARThHTW (passive singular) seems to
have 5 subject nominatives. One of my students this morning tried to
suggest that since each of these nominatives is singular they individually
agree with the verb. But I just can't get past the four kai's which (I
think) produces a compound of subjects (which has to be plural). Right?

Looking at this another way, is it possible to take the first
nominative as the subject of the verb, place them together in translation,
and then to translate the rest of the nominatives in a sort of appended
manner (for each of which the same verb would then be implied)? The
prepositional phrase SUN PASH KAKIA would suggest the same appended
relationship to the main subject and verb anyway. Thus we would have a
translation along this line: "Let all bitterness be put away from you (and
the same with) all wrath and anger and clamor and blasphemy, with all evil."

Would this make more sense of the singular verb, or have I twisted
another rule
of syntax to solve the first problem?

b) In Eph.5:1 the first and primary clause is a predicate-nominative
construction, and the second clause (`WS TEKNA 'AGAPHTA) is a comparative
clause. None of my lexical sources or grammars gave me helpful information
about `WS. Are the words "beloved children" nominatives or accusatives?
Does `WS require them to be accusative or not? The relationship of this
second clause, dependent as it is on the first clause suggests that "beloved
children" could legitimately be predicate nominatives along with MIMHTAI.
Anybody know?